Technical Field
The present disclosure relates to an ultra high resolution flat panel display having an in-cell type touch sensor. Specifically, the present disclosure relates to an ultra high resolution flat panel display having the in-cell type touch sensor in which the parasitic capacitance between the touch electrode and the routing line is reduced and the storage capacitance between the common electrode and the pixel electrode can be ensured enough.
Discussion of the Related Art
Recently, as increasing the needs for display representing the various multimedia data, the flat panel displays are developed in large area with low price and high quality (high video quality, ultra high resolution, increased brightness, real color representation ability, etc.). These flat panel displays are equipped with various input devices for interfacing with the user, including keyboard, mouse, track-ball, joy-stick, digitizer, and so on.
However, the above mentioned input devices should have enough space for installing into the display and for working space. Further, sometimes the users have to learn how to use these input devices. Therefore, easy and simple input devices for the display are required. One solution is the touch sensor by which the user can input information directly on the screen of the display with fingers or a touch pen while seeing the display.
The touch sensor has less errors and simple structure. User can input and/or select his/her instructions by simply touching the screen of the display without any input devices, easily and quickly. With this easiness, the touch sensors are applied to the various display system.
According to the structure, a touch sensor can be categorized into the add-on type, the on-cell type, and the integrated type (or in-cell type). In the add-on type touch sensitive display, the touch sensor is attached on the top surface of the display after the display and the touch sensor are manufactured separately. In the on-cell type touch sensitive display, the elements for the touch sensor are formed on the top substrate of the display, directly. In the in-cell type touch sensitive display the elements for the touch sensor are manufactured into the display panel. Therefore, the in-cell type can be much thinner than other types of touch sensitive displays and has a much longer life time and endurance.
Especially, for the in-cell type, since the common electrode of the display pixels can be used as the touch electrode of the touch sensor, the thickness of the display having touch sensor can be thinner. As the elements for the touch sensors are formed into the display device, the touch sensor can endure a large number of touch actions. Nowadays, the in-cell type is prevalent among the touch sensors embedded in display systems.
The in-cell type touch sensor can be categorized into the photo type and the capacitance type in accordance with the sensing method. Further, the capacitance type can be divided into the self capacitance type and the mutual capacitance type.
The self capacitance type is that a plurality of patterns are formed at the touch area and the variations of the capacitance of each pattern are detected for deciding where the touch occurred. The mutual capacitance type is one where a matrix type array of the X-axis electrodes and the Y-axis electrodes are formed at the touch area, and the touch action can be detected by applying the driving pulse to the X-axis electrode and by detecting the variations of the voltage at the sensing nodes from the Y-axis electrodes. The sensing nodes can be defined by the crossing point of the X-axis electrodes and the Y-axis electrodes.
However, for the mutual capacitance type touch sensor, the amount of the mutual capacitance generated at sensing the touch is low, but the parasitic capacitances between the gate line and the date line included into the display are high. Therefore, it may be hard to exactly decide where the touch action is detected, due to the interference of the parasitic capacitance.
Further, for the multi touch sensing, the mutual capacitance type touch sensor should have a plurality of touch driving lines for touch driving and a plurality of touch sensing lines for touch sensing on the common electrode. Therefore, the line structure would be very complicated.
Having the high touch resolution with the simple line structure, the self capacitance (type) touch sensor is more widely used than the mutual capacitance touch sensor.
FIGS. 1 and 2, illustrate a liquid crystal display having the self capacitance touch sensor (or, ‘touch sensor embedded display’) according to the related art. FIG. 1 is a plane view illustrating the structure of the touch sensor embedded in a display according to the related art. FIG. 2 is a plane view illustrating the enlarged part having two touch electrodes (Tx) denoted as {circle around (a)} in FIG. 1.
Referring to FIG. 1, the display having the self capacitance touch sensor has the display area AA and the non-display area (or ‘bezel area’) NA. The display area AA is the area in which the touch electrodes used as the common electrode are formed and the video information is represented. The non-display area NA surrounding the display area AA is the area in which various lines and the touch driving circuit IC are formed.
The display area AA includes a plurality of touch electrodes Tx arrayed along to the first direction (for example, X-axis) and the second direction (for example Y-axis) crossing to the first direction, and a plurality of routing line TW along to the second direction. For example, the touch electrodes Tx may be arrayed in a matrix manner of N block×M block (N rows×M columns).
The plurality of touch electrodes Tx arrayed in the display area AA may be formed by dividing the common electrode of the liquid crystal display. During the display mode, for representing the video data, a common electrode can work as the common electrode. During the touch driving mode, for sensing touch action, the common electrode can work as the touch electrode.
FIG. 2 illustrates an area where two neighboring touch electrodes Tx in the vertical direction (the second direction, or Y-axis). At one touch electrode Tx, a plurality of pixel area PA may be allocated. In FIG. 2, the nine pixel areas PA arrayed in a 3×3 matrix manner are allocated at each touch electrode Tx. However, more pixel areas PA can be allocated at each touch electrode Tx.
Any one pixel area PA is defined by the crossing structure of the gate line GL running along the first direction (or X-axis direction) and the data line DL running along the second direction (or Y-axis). In the pixel area PA, main elements for the display are disposed. In the example of the liquid crystal display of FIG. 2, a thin film transistor T connected to the gate line GL and the data line DL and the liquid crystal cell LC driven by the thin film transistor T may be disposed.
In each pixel area PA, one pixel electrode PXL is disposed. The pixel electrode PXL is connected to the thin film transistor T and is applied with a driving voltage corresponding to the video information via the data line DL. For driving the liquid crystal cell LC by the driving voltage applied to the pixel electrode PXL, the common electrode COM is disposed as facing the pixel electrode PXL. The common electrode COM may be disposed in each pixel area PA individually. On the other hand, for the driving stability of the liquid crystal cell LC, it is prefer that the common electrodes of all pixel areas are commonly connected.
When touch electrode Tx is formed, to simplify the structure, the touch electrode Tx may be used as the common electrode COM. Here, each common electrode COM is formed as covering every 9 pixel areas PA. Further, these common electrodes are used as the touch electrode Tx.
All pixel areas PA are grouped into 3×3 matrix manners, each common electrode COM covering every 3×3 pixel areas PA can be designed as each touch electrode. For example, as shown in FIG. 2, the first common electrode covering the first group of 3×3 pixel areas PA can be defined as the 1row 1column touch electrode T11. The common electrode covering the right neighboring group of 3×3 pixel areas PA can be defined as the 1row 2column touch electrode T12. The common electrode covering the lower side neighboring group of 3×3 pixel area PA can be defined as the 2row 1coloumn touch electrode T21, and the common electrode covering the diagonal side neighboring group of 3×3 pixel area PA can be defined as the 2row 2column touch electrode T22.
Each touch electrode Tx may have one routing line TW. For example, the 1row 1column touch electrode T11 connects to the 1row 1column routing line TW11. The 2row 1column touch electrode T21 connects to the 2row 1column routing line TW21. The routing lines TW may be disposed as overlapping with the data line DL with an insulating layer there-between. Otherwise, the routing lines TW may be disposed at the same layer with the data line DL with a predetermined distance from the data line DL. In that case, the aperture ratio may be reduced.
The non-display area NA surrounds the display area AA and includes the integrated circuit for data driving and touch driving IC and various lines. The integrated circuit for data driving and touch driving IC drives the gate lines GL, supplies the video data to the data line DL and supplies the common voltage to the touch electrode Tx (the common electrode) at the display mode. Further, during the touch mode, the integrated circuit IC for data driving and touch driving supplies the touch driving voltage to the touch electrode Tx. By scanning the variations of the capacitance at the touch electrode Tx, it is decided that which touch electrode Tx is touched.
The various lines include the routing lines TW connected to each touch electrode Tx and the gate lines GL and the data lines DL connected to the integrated circuit for data driving and touch driving IC.
FIGS. 3 and 4 illustrate the connecting structure of the touch electrode and the routing line in the liquid crystal display having the self capacitance touch sensor. FIG. 3 is a plan view illustrating an enlarged area including two neighboring pixels denoted as {circle around (b)} in FIG. 2 according to the related art. FIG. 4 is a cross section view, along the cutting line I-I′ of FIG. 3, illustrating the structure of the liquid crystal display having the self capacitance touch sensor according to the related art.
Referring to FIGS. 3 and 4, the liquid crystal display having the self capacitance touch sensor according to the related art includes a plurality of pixel areas PA arrayed in a matrix manner by the crossing structure of the gate line GL and the data line DL on the substrate SUB. Each of the pixel areas PA includes a thin film transistor T, a pixel electrode PXL connected to the thin film transistor T, and a common electrode COM facing with the pixel electrode PXL.
The thin film transistor T may have the double gate structure in which the semiconductor layer is overlapped with the gate line GL twice so that two channel areas A are formed. On the substrate SUB, a light shielding layer LS may be formed where the channel area A is disposed. On the light shielding layer LS, a buffer layer BUF is deposited as covering the whole surface of the substrate SUB. On the buffer layer BUF, a semiconductor layer is disposed where the light shielding layer LS is formed. On the semiconductor layer, a gate line GL and the gate electrode G are disposed with a gate insulating layer GI.
One side of the semiconductor layer is connected to the date line DL. The semiconductor layer has a ‘U’ shape so as to cross the gate line GL twice. The overlapped portion of the gate line GL with the semiconductor layer would be the gate electrode G. The portions of the semiconductor layer overlapped with the gate electrode G would be the channel area A. On the whole surface of the substrate SUB having the gate line GL and the gate electrode G, an intermediate insulating layer IN is deposited.
On the intermediate insulating layer IN, data line DL is disposed. One portion of the data line DL is connected to the one side of the semiconductor layer. The other side of the semiconductor layer is connected to the drain electrode D. Here, the source electrode S is not formed separately but is defined as the portion of the data line DL overlapped with the semiconductor layer. The drain electrode D may be formed separately. Otherwise, one portion of the pixel electrode PXL connected to the other side of the semiconductor layer may be the drain electrode D.
On the whole surface of the substrate SUB having the thin film transistor T including the gate electrode G, the source electrode S and the drain electrode D, a planar layer PAC is deposited. On the planar layer PAC, the common electrode COM is disposed. In order to be used as the touch electrode Tx, the common electrode COM may be patterned as covering the grouped pixel areas. Further, the common electrode COM, also being the touch electrode Tx, preferably has the open structure in which it does not cover the pixel contact hole PH exposing the drain electrode D.
On the whole surface of the substrate SUB having the common electrode COM, a first passivation layer PAS1 is deposited. On the first passivation layer PAS1, a routing line TW (e.g., TW11) is formed. In order to ensure enough aperture ratios, the routing line TW is preferably overlapped with the data line DL. On the whole surface of the substrate SUB having the routing line TW, a second passivation layer PAS2 is deposited. Each routing line TW is connected to one touch electrode Tx. Therefore, by patterning the second passivation layer PAS2 and the first passivation layer PAS1, the touch contact hole TH exposing one portion of the touch electrode Tx and the routing contact hole WH exposing one portions of the routing line TW are formed.
On the second passivation layer PAS2, the pixel electrode PXL is formed. The pixel electrode PXL connects to the drain electrode D of the thin film transistor T through the pixel contact hole PH. Within the pixel area PA, the pixel electrode PXL is disposed as overlapping with the common electrode COM with the second passivation layer PAS2 and the first passivation layer PAS1 there-between. Here, using the same material with the pixel electrode PXL, the touch connecting terminal TT is formed. The touch connecting terminal TT electrically/physically connects the touch electrode Tx exposed through the touch contact hole TH to the routing line TW exposed through the routing contact hole WH.
Like this, the routing line TW extends along to the second direction, e.g., Y axis. Therefore, any one routing line TW may overlap with the touch electrodes Tx arrayed along the Y-axis. For example, 2row 1column routing line TW21 connects to the 2row 1column touch electrode Tx21 and overlaps with other touch electrodes Tx arrayed at lower side from the 2row 1column touch electrode Tx21 along to the Y-axis with the first passivation layer PAS1 there-between.
When the parasitic capacitance between the 2row 1column routing line TW21 and other touch electrodes Tx, the sensing accuracy may be lowered. Therefore, it is required that a high insulating property should be ensured between the touch electrode Tx and the routing line TW. For example, it is preferable that the first passivation layer PAS1 has a thickness of 2,000 Å or more to reduce the electrostatic noise between the touch electrode Tx and the routing line TW. In that case, however, the capacitance between the pixel electrode PXL and the common electrode COM are also lowered so that the storage capacitance may be reduced. As the result, the high speed touch sensing is not possible.
Further, as shown in FIG. 3, when forming the contact holes TH and WH for connecting the touch electrode Tx and the routing line TW, the contact hole may be required to have enough area for ensuring good contact. In order to prevent reduction of aperture ratio, it is preferable that the contact holes TH and WH are disposed as being overlapped with the lines or close to the lines. However, in the ultra high density structure, the area of the pixel area PA is smaller and the elements are closer, so that it is very hard to ensure the area of the contact hole for good contact.
As mentioned above, for the in-cell touch type flat panel display, especially for the ultra high density display, the contact hole connecting the touch electrode and the routing line has the minimum open area and the minimum disposed area. To do so, it is required to develop an in-cell type touch panel embedded flat panel display having different structure than the related art.